Conforming an array of enums to Hashable for use as dictionary key

I'd like to use an array of custom enums as a dictionary key, but I'm having difficulty figuring out how to make the array conform to Hashable. The compiler tells me that [Symbol] doesn't conform to Hashable. What do I have to do to get this to compile?

I messed around with an extension to Array where Element:Symbol, but I couldn't figure out how to add a protocol that way.